County outline
Where Allen County is located
Area breakdown
Land accounts for 99% of Allen County’s measured area and water for 1%. Its combined area converts to 1,308.8 square kilometers or approximately 323,409 acres.
Green: land · blue: water
| Measurement | Square miles | Square kilometers | Acres |
|---|---|---|---|
| Land | 500.298 | 1,295.766 | 320,190.7 |
| Water | 5.028 | 13.022 | 3,217.9 |
| Total | 505.326 | 1,308.788 | 323,408.6 |
How Allen County compares
By original Census land area, Allen County ranks #97 of 105 in Kansas and #2081 of 3,222 nationally. National rankings include the 50 states, District of Columbia, and Puerto Rico.
Its land area is 0.686 times the Kansas county-equivalent median of 729.7 square miles. It accounts for 0.6% of the combined county land area in the state.
See the complete Kansas ranking · What counts as a county equivalent?
Population and density of Allen County
The Census Bureau estimates that 12,302 people lived in Allen County on July 1, 2025. That ranks #2,338 of 3,222 county equivalents nationally and #36 of 105 in Kansas. Since the April 1, 2020 estimates base of 12,521, the population has declined by 219 (−1.7%), compared with +1.3% for Kansas as a whole.
With 500.3 square miles of land, that is 25 people per square mile (9.5 per km²), placing Allen County #2,155 nationally for density and #31 in Kansas. The median county equivalent has 47 people per square mile; the Kansas median is 8.1. Put another way, there are about 26 acres of land per resident.
| July 1 | 2020 | 2021 | 2022 | 2023 | 2024 | 2025 |
|---|---|---|---|---|---|---|
| Estimate | 12,533 | 12,501 | 12,469 | 12,454 | 12,361 | 12,302 |
| Change | — | −32 | −32 | −15 | −93 | −59 |
U.S. Census Bureau, Vintage 2025 population estimates. Estimates are revised each year and are not decennial census counts. Density divides the whole population by the whole county’s land area, so it describes an average, not how settlement is distributed within the county. Population sources and methods.
Cities and towns in Allen County
8 incorporated places lie at least partly in Allen County. Together they are home to 8,597 people (69.9%); the other 3,705 (30.1%) live outside any incorporated place, in unincorporated communities and rural areas.
The largest is Iola city, with 5,240 residents in the county.
| Incorporated place | Population 2025 | Since 2020 | Land mi² |
|---|---|---|---|
| Iola cityCounty seat | 5,240 | −2.9% | 4.847 |
| Humboldt city | 1,807 | −2.1% | 1.61 |
| La Harpe city | 481 | −0.6% | 0.797 |
| Gas city | 467 | −1.1% | 0.72 |
| Moran city | 455 | −2.2% | 0.419 |
| Savonburg city | 75 | 0% | 0.192 |
| Elsmore city | 52 | −1.9% | 0.152 |
| Bassett city | 20 | −4.8% | 0.067 |
Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each place inside Allen County. Land: 2026 Census Gazetteer, for the whole place even where it extends into other counties. How communities are listed.
Metropolitan area
Allen County is not part of any metropolitan or micropolitan statistical area in the Office of Management and Budget’s July 2023 delineation; 1,306 other county equivalents are also outside one. These areas are built around an urban core of at least 10,000 people plus the counties tied to it by commuting, so counties outside them are generally rural.
ZIP codes
12 ZIP Code Tabulation Areas have land in Allen County; 7 of them have most of their land inside the county, and the others mainly cover neighboring areas.
660156603966716667206673266742667486674966751667556675866772
ZIP Code Tabulation Areas are the Census Bureau’s approximations of USPS ZIP Code service areas, from the 2020 Census relationship files. Lighter codes have less than half of their land in this county. Post-office-box and single-address ZIP Codes have no tabulation area.
Counties bordering Allen County
Allen County shares a land border with 4 county equivalents. It has more land than 1 of them. The largest neighbor is Bourbon County (635.5 mi²) and the smallest is Woodson County (497.8 mi²). Together with its neighbors, Allen County forms a block of 2,784.7 mi² of land, of which it holds 18%.
| Bordering county equivalent | Land mi² | Size vs. Allen | Compare |
|---|---|---|---|
| Bourbon County | 635.5 | 1.3× larger | Compare |
| Anderson County | 579.6 | 1.2× larger | Compare |
| Neosho County | 571.5 | 1.1× larger | Compare |
| Woodson County | 497.8 | about the same | Compare |
How big is Allen County compared with U.S. states?
Allen County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 2.1 times as much. Kansas’s county land could hold about 163 areas the size of Allen County.
Another way to picture it: the same land area would fill a square about 22.4 miles (36 km) on each side. Real county shapes are rarely square, so this is a scale reference rather than a width or driving distance.
State figures are the sums of each state’s county-equivalent land measurements in the same Census release, so states and counties are compared on the same basis. Published state totals can differ slightly because of rounding. Compare all states · Counties bigger than entire states.
What stands out about Allen County?
Allen County has more land than 1,141 of the other 3,221 county equivalents in the dataset.
A median is the middle county-equivalent measurement, not the average of the largest and smallest. All three bars use the same linear scale. Very small areas may appear as a thin sliver; the labels retain their values.
Does including water change its rank?
Using land plus water places Allen County at #2,158 nationally by total area, 77 places farther from the top than its land rank. Other county equivalents gain more area when their water measurements are included.
Its water share is 1%, compared with a national county-equivalent median of 1.2% — 0.2 percentage points lower. This describes the statistical geography’s land/water mix, not flood exposure or developable land.
Closest positions in the national land ranking
These entries sit immediately beside Allen County in the national ranking. They can be in different states and are not necessarily geographic neighbors.
| Land rank | County equivalent | Land mi² | Comparison |
|---|---|---|---|
| #2080 | Floyd County, Iowa | 500.6 | Compare |
| #2081 | Allen County, Kansas | 500.3 | This county |
| #2082 | Grayson County, Kentucky | 499.5 | Compare |
Calculated from the same Census release as the area table. Total-area order uses original ALAND + AWATER; water shares and chart labels use published square miles. Calculation details.
Representative coordinates
The Census internal point is 37.884228, -95.300945. It represents a location inside the geography; it is not necessarily the centroid or the address of a courthouse.
Source and precision
U.S. Census Bureau, 2026 Gazetteer Files, Counties. Original ALAND: 1,295,764,699 m²; AWATER: 13,021,461 m². Rankings use ALAND; exact ties use ascending GEOID. Tables preserve Census-published square miles to three decimals, with conversions based on those values.
Common questions
How big is Allen County?
Allen County, Kansas has 500.3 square miles (1,295.8 km²) of land and 5.028 square miles of water, for a total area of 505.3 square miles. It ranks #2081 of 3,222 U.S. county equivalents by land area.
Is Allen County the largest county in Kansas?
No. Allen County ranks #97 of 105 in Kansas by land area. The largest is Butler County, with 1,429.7 square miles of land.
What counties border Allen County?
Allen County shares a land border with Neosho County, Anderson County, Woodson County, and Bourbon County.
What is the population of Allen County?
The Census Bureau estimates Allen County had 12,302 residents on July 1, 2025, ranking #2,338 of 3,222 county equivalents. That is 25 people per square mile of land.
What is the county seat of Allen County?
The county seat of Allen County is Iola.
What cities and towns are in Allen County?
Allen County has 8 incorporated places. The most populous five are Iola city, Humboldt city, La Harpe city, Gas city, and Moran city; 3,705 residents live outside any incorporated place.
Is Allen County part of a metropolitan area?
No. Allen County is outside every metropolitan and micropolitan statistical area in the July 2023 OMB delineation.
How many ZIP codes are in Allen County?
12 ZIP Code Tabulation Areas have land in Allen County, and 7 of them have most of their land inside the county. Census ZIP Code Tabulation Areas approximate USPS ZIP Code areas.
How does Allen County compare with U.S. states?
It has less land than every state. Rhode Island, the smallest, has 2.1 times as much land.
How many acres of land are in Allen County?
The land measurement converts to approximately 320,191 acres. Including water, total area is approximately 323,409 acres. One square mile equals 640 acres.
Why might another source show a different area?
Check whether it reports land or total area, its Census vintage, and its rounding. Our guide explains how to reconcile county area figures.
Can this establish a property boundary?
No. Statistical measurements and generalized maps do not establish property lines. Consult the relevant local surveying or land-records authority.